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Physics Astrophysics

astro-ph Watch Astrophysics

Monday 15 June

Solar and Stellar Astrophysics

KRONOS II: Solar-like Umbra and Penumbra Properties on the Young Sun V1298~Tau

Matthew M. Murphy, Adina D. Feinstein, Meir E. Schochet et al. (+14 more)

Transiting exoplanets provide a unique laboratory for studying stellar surface heterogeneities via starspot or facular occultations. When observed at multiple wavelengths, this configuration enables spectroscopic characterization of spot thermal contrasts, distributions, and morphology. In this work, we leverage JWST NIRISS/SOSS transit observations of the 20–30~Myr planets V1298~Tau~bcd to study the surface properties of their solar analog host star V1298~Tau. We identify 14 starspot crossing events across two visits. We derive $0.8-2.8\mu$m starspot contrast spectra and demonstrate the contrasts can only be explained when accounting for the umbral and penumbral components of the starspots, robust to which stellar model grid is assumed. The spot temperatures are broadly consistent between visits, suggesting that V1298~Tau ($T_\mathrm{phot}=4866\pm33$\,K) has starspots with $T_{\mathrm{umbra}}$ = 3300–3600\,K umbrae and $T_{\mathrm{penumbra}}$ = 4400–4600\,K penumbrae, and are $\sim$25–30% umbrae by area. The differences between these spot components and the stellar photosphere are consistent with sunspots. Additionally, the relation between the spot contrast and the ratio of umbral to penumbral area is similar to that of the Sun. Combining these JWST observations with long baseline multi-band photometry from the Las Cumbres Observatory, we also estimated the global unocculted spot distribution, revealing at least 5 additional large unocculted active regions. Altogether, these measurements suggest that while the total spot coverage evolves in time, the relative temperatures of surface heterogeneities on Sun-like stars may be consistent throughout their lifetimes. Furthermore, these results demonstrate that JWST exoplanet transit observations can be useful for starspot substructure characterization.
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All authors Matthew M. Murphy, Adina D. Feinstein, Meir E. Schochet, Benjamin V. Rackham, Luis Welbanks, Darryl Z. Seligman, Girish M. Duvvuri, Eva-Maria Ahrer, John H. Livingston, Saugata Barat, Jean-Michel Désert, Rafael Luque, Catriona Murray, Matthew C. Nixon, Sydney Petz, Michael Radica, Hinna Shivkumar

Earth and Planetary Astrophysics

The 3D Architecture of a pair of 6:1 Resonant Brown Dwarfs around the Naked-eye star $\nu$ Ophiuchi

Tianshenhong Sang, Guang-Yao Xiao, Ying-Yi Cao et al. (+8 more)

We present a revisiting study of the brown dwarf pair orbiting the naked-eye ($V=3.3$) K-giant $\nu$~Ophiuchi, located only 44\,pc from our Solar system. By jointly analysing archival radial-velocity measurements together with astrometric data from Hipparcos and the Gaia second and third data releases, we determine the three-dimensional architecture of the system and robustly constrain the masses of both companions. We find brown dwarf masses of $m_{\mathrm{b}} = 24.2^{+6.4}_{-2.8}\,M_{\mathrm{J}}$ and $m_{\mathrm{c}} = 26.8^{+4.3}_{-2.9}\,M_{\mathrm{J}}$. The mathematical constraint, derived from the posterior distribution of the mutual inclination based on MCMC samples, yields a mutual inclination of $\psi_{\mathrm{bc}}=46^{+27}_{-24}\!\,^{\circ}$, while direct calculations based on the maximum a posteriori and posterior median orbital parameters yield values of $\sim$$10^{\circ}$ and $\sim$$20^{\circ}$, respectively. Resonance analysis indicates that the two companions can still be trapped in a 6:1 mean-motion resonance in the maximum a posteriori configuration. To place an upper limit for the mutual inclination, dynamical stability analysis over a 1~Myr timescale further constrains it to be no larger than $\sim$$15^{\circ}$. Systems hosting brown dwarf pairs are rare, yet they provide important constraints on theories of planetary formation and dynamical evolution. Current detections suggest that brown dwarf pairs preferentially reside at large separations from their host stars and are more common in less mature systems. This supports a star-like formation pathway via gravitational instability in disk.
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All authors Tianshenhong Sang, Guang-Yao Xiao, Ying-Yi Cao, Huan-Yu Teng, Yu-Juan Liu, Wei Wang, Fan Liu, Fei Zhao, Meng Zhai, Fabo Feng, Shang-Fei Liu

Astrophysics of Galaxies

The Edge-on Galaxies in the DESI survey (EGIDE): sample building and photometry

Alexander A. Marchuk, Sergey S. Savchenko, Dmitry I. Makarov et al. (+7 more)

We present the EGIDE (The Edge-on Galaxies in the DESI survey) project - a catalogue of 149,215 edge-on galaxy candidates created using the data of the DESI Legacy Imaging Survey DR10 images. The catalogue size is ten times bigger than its predecessor and covers more than half of the sky. It is constructed in an automatic way utilizing the full power of manual annotations from the GalaxyZoo volunteers, implemented in the Zoobot neural model, which was fine-tuned to search for edge-on galaxies specifically. To ensure the credibility of the dataset, subsequent manual supervision was done. The EGIDE catalogue provides homogeneous SExtractor photometry in $griz$ bands, total stellar mass estimation, redshift values for 98% of the sample, star formation rates and other information. All of this is publicly available at The Edge-on Galaxy Database site. The preliminary analysis focused on differences between edge-on galaxies in the so-called blue sequence and red cloud populations. These galaxies demonstrate distinct properties: the number of redder galaxies drops with increasing $a/b$ ratio faster than for the bluer galaxies; galaxy thickness varies with galaxy colour: red sequence galaxies are thicker than blue cloud galaxies; the flattening ratio $q=b/a$ increases with total stellar mass $M_{\star}$ for the high-mass end. It is an intriguing result, that the same trend of $q$ increasing is detected from both the statistical models of figures of revolution and direct observations of edge-on galaxies in EGIDE independently. The full extent of the validity of this relationship can only be determined after correctly accounting for the contributions of the bulge and the PSF.
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All authors Alexander A. Marchuk, Sergey S. Savchenko, Dmitry I. Makarov, Vladimir P. Reshetnikov, Ilia V. Chugunov, Matvey D. Kozlov, Aleksandra V. Antipova, Anastasia M. Sypkova, Evgenii V. Rubtsov, Dmitry V. Bizyaev

Cosmology and Nongalactic Astrophysics

Revisiting the Lyth bound constraints on inflation from ACT DR6 results

Rui Yang, Jun Tao, Peng Wang et al. (+1 more)

The Lyth bound asserts that the field excursion of inflaton must be sub-Planckian, thereby imposing an upper bound on the amplitude of the tensor power spectrum in inflationary scenario. This bound is conventionally derived assuming a scale-invariant curvature power spectrum, i.e., $n_s = 1$. However, astrophysical observations confirm a red-tilted spectrum with $n_s < 1$. In light of recent results from the Atacama Cosmology Telescope (ACT) DR6, we revisit these constraints using the newly implied scalar spectral index of $n_s \simeq 0.9743$. Incorporating the ACT data yields a different upper bound on the tensor-to-scalar ratio $r$, which can potentially exclude inflationary scenarios previously robust under the original Lyth bound with $n_s = 1$. Our result highlights the urgent need to combine theoretical Lyth bound considerations with the most up-to-date astrophysical data.
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All authors Rui Yang, Jun Tao, Peng Wang, Mian Zhu

Cosmology and Nongalactic Astrophysics

Interactions in the dark sector: intrinsic entropy couplings

Elsa M. Teixeira

We present a new class of interacting dark sector models in which the intrinsic entropy of a dark matter fluid couples to a scalar field describing dark energy. These interactions are constructed within a covariant Lagrangian framework, including algebraic and derivative entropy couplings, effectively leading to pure momentum exchange in the dark sector. A key feature is that the background cosmology remains unchanged and therefore indistinguishable from $\Lambda$CDM or uncoupled quintessence. However, at the level of the linear perturbations, the dark matter Euler equation exhibits scale-dependent contributions, while the continuity equation is unmodified. We show that these classes of models are compatible with current CMB constraints and can potentially produce observable signatures in large-scale structure.
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Astrophysics of Galaxies

Simulating winds in the Galactic centre: I. Supernova-driven multiphase outflows and HI cloud acceleration

Nicolas Peschken, Enrico M. Di Teodoro, Michał Hanasz et al. (+5 more)

The centre of the Milky Way (MW) hosts powerful multiphase outflows, as evidenced by the Fermi and eROSITA bubbles, and by cold atomic hydrogen (HI) gas clouds detected up to a few kiloparsecs above the disc. In this paper, we investigate the process of launching gaseous outflows in the nuclear region of our Galaxy from supernova feedback. Using the PIERNIK code, we perform a simulation of the Galaxy with 3 pc resolution in both the Central Molecular Zone (CMZ) and the surrounding outflows. Our model follows the entire gas dynamics, from accretion onto the central star-forming ring through the dust lanes to star formation, feedback and the launching of outflows. Star formation occurs in cycles of starbursts followed by quiescent periods, mainly driven by intermittent gas inflows along the dust lanes. Stellar feedback generates hot ($\sim 10^7$ K) winds launched from the CMZ at velocities of order 1000 km/s, as well as colder ($\sim 10^4$ K) Hi gas clouds with velocities of $\sim 100$ km/s at heights of 1 - 2 kpc from the mid-plane. The spatial distribution, kinematics, and masses of our simulated clouds are broadly consistent with observations. Their properties indicate that they are accelerated out of the disc by entrainment from the hot phase. At least 20% of these clouds return to the disc in fountain flows, while the majority are disrupted by interaction with the hot phase. While periods of intense star formation and supernova activity lead to more numerous outflowing clouds with higher masses and densities, quiescent phases with star formation rates close to that observed in the CMZ still produce Hi clouds consistent with data. These results suggest that stellar feedback alone, operating in a time-variable nuclear environment, can account for the observed population of cold clouds in the Galactic centre outflow.
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All authors Nicolas Peschken, Enrico M. Di Teodoro, Michał Hanasz, Lucia Armillotta, Robin Tress, Thorsten Naab, Dominik Wóltański, Artur Gawryszczak

Astrophysics of Galaxies

The Narrow-Line Seyfert 1 Phenomenon: Accretion State Versus Host Galaxy Properties

Kaizheng Guo, Hassen M. Yesuf, Lei Hao et al. (+3 more)

The physical origin of the narrow-line Seyfert 1 (NLS1) and broad-line Seyfert 1 (BLS1) dichotomy remains debated, with competing scenarios invoking host-galaxy evolution or intrinsic accretion physics. We analysed host-galaxy properties and AGN luminosities obtained from CIGALE spectral energy distribution fitting for $\sim$12,000 Type 1 AGNs from the Sloan Digital Sky Survey, of which 29% are NLS1s. Globally, NLS1s have lower virial black hole masses, higher inferred Eddington ratios, lower stellar masses, and higher specific star formation rates than BLS1s. In the FWHM(\Hb)–$L_{\rm AGN}$ plane, the conventional 2000 km s$^{-1}$ boundary is better viewed as an empirical division within a continuous parameter space rather than a physical threshold, with Fe~II tracing the high-accretion end. In a host-matched subsample of 767 NLS1–BLS1 pairs with statistically indistinguishable stellar mass, black hole mass, and redshift, NLS1s still show higher Eddington ratios, stronger Fe~II emission, and bluer optical continua, together with elevated SFR and dust attenuation, suggesting that the NLS1 phenomenon is most naturally associated with a high-accretion state within the continuous distribution of Type 1 AGNs, while host-galaxy gas supply may also play a role in modulating its strength. In this picture, NLS1 and BLS1 classifications reflect different locations within a continuous accretion sequence of the same underlying population rather than two physically disjoint classes.
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All authors Kaizheng Guo, Hassen M. Yesuf, Lei Hao, Vineet Ojha, Lin Lin, Zhenzhen Li

Instrumentation and Methods for Astrophysics

Scalable Bayesian data curation for next-generation radio experiments

S. A. K. Leeney, E. de Lera Acedo, W. J. Handley et al. (+42 more)

Next-generation radio telescopes produce data volumes that preclude manual quality assessment, yet data curation remains essential for science. We present a general, fully automatic Bayesian anomaly-detection method for radio science experiments in which data curation is performed inside the inference: a latent anomaly indicator is marginalised in the likelihood rather than converted into an external pre-flag. Implemented in JAX with GPU-accelerated inference, the pipeline assigns probabilistic data-curation scores without prior knowledge and requires no thresholds, manual inspection, or subjective decisions. We demonstrate the method on the Radio Experiment for the Analysis of Cosmic Hydrogen (REACH), applying it to 4655 observations (one year of REACH data). The pipeline assigns scores across time and frequency, enabling identification of the optimal observations to carry forward into scientific inference while reducing the risk that contaminated data bias the result. In doing so, it simultaneously recovers weather-driven systematics, instrument-component drifts, and narrow-band radio-frequency interference, while revealing complex dependencies between data quality and environmental or instrumental state that would be difficult to uncover by manual curation alone. This turns data curation from an external manual bottleneck into autonomous, inference-level infrastructure for the Square Kilometre Array era.
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All authors S. A. K. Leeney, E. de Lera Acedo, W. J. Handley, H. T. J. Bevins, G. Allen, D. Anstey, K. Artuc, G. Bernardi, M. Bucher, S. Carey, J. Cavillot, R. Chiello, A. S. Chu, W. Croukamp, J. Cumner, S. Dasgupta, A. K. Dash, D. I. L. de Villiers, J. Dhandha, A. Dragovic, J. A. Ely, A. Fialkov, T. Gessey-Jones, C. Kirkham, G. Kulkarni, A. Magro, P. D. Meerburg, S. Mittal, D. Molnar, R. S. Patel, J. H. N. Pattison, S. Pegwal, C. M. Pieterse, J. R. Pritchard, G. M. Z. Rajpoot, N. Razavi-Ghods, D. Robins, I. L. V. Roque, A. Saxena, K. H. Scheutwinkel, E. Shen, P. H. Sims, M. Spinelli, J. L. Tutt, J. Zhu

Cosmology and Nongalactic Astrophysics · Cross-listed from cs.LG

Neural Bayesian Anomaly Mitigation: A Robust Loss that Doubles as an Unsupervised Contamination Classifier

S. A. K. Leeney, W. J. Handley, H. T. J. Bevins et al. (+1 more)

Engineered robust losses such as Huber, Student-$t$, and generalised cross-entropy make supervised models tolerant of contamination but cannot answer which observations are corrupted. We introduce Neural Bayesian Anomaly Mitigation (NBAM), a general-purpose drop-in loss derived from a Bayesian latent-switch mixture model: the marginal likelihood defines a robust supervised loss, and the associated posterior defines an unsupervised contamination classifier. Like Huber or Student-$t$, NBAM can replace the standard training loss in any supervised pipeline; unlike them, it additionally learns a structured contamination model and returns a calibrated per-sample contamination posterior. A learned input-dependent prior $\pi_\phi(x)$ captures the spatial locality of contamination, so that samples near known corruptions are more likely to be flagged, while an Occam penalty emerges automatically and regularises against over-flagging. On CIFAR-10 with asymmetric label contamination, NBAM recovers the structure of the corruption process without supervision: the contamination posterior separates clean from corrupted samples, and the learned anomaly head identifies the direction of every label-flip pair. Alongside these capabilities, NBAM outperforms the four robust-loss baselines considered here at contamination rates 0.2-0.6.
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All authors S. A. K. Leeney, W. J. Handley, H. T. J. Bevins, E. de Lera Acedo

Cosmology and Nongalactic Astrophysics

A First Post-Friedmann Extension of the Schrödinger Approach to Cosmic Structure Formation

Yiwen Deng-Huang, Daniele Bertacca and Sabino Matarrese

We extend the Schrödinger approach to large-scale structure formation beyond the Newtonian regime by working at first post-Friedmann (1PF) order. The standard Schrödinger–Poisson system gives a useful reformulation of the dynamics of a self-gravitating pressureless fluid, but it corresponds to the leading post-Friedmann, or Newtonian, limit. It therefore misses the relativistic corrections that enter at next-to-leading order and become relevant on horizon scales and for high-precision cosmological surveys. Starting from the 1PF continuity and Euler equations in a flat $\Lambda$CDM background, we identify the conserved density variable associated with covariant mass conservation. In terms of this variable, the continuity equation takes a Newtonian-like conservative form. However, even for vanishing covariant vorticity, the spatial velocity field in the cosmological frame contains a transverse 1PF component. Thus the full 1PF mass flux cannot be represented solely by the gradient of a scalar phase. We show that the Schrödinger-like formulation at 1PF order requires an effective vector potential fixed by this transverse velocity component. This vector potential contains the post-Friedmann metric vector perturbation, related to relativistic frame-dragging effects, together with nonlinear scalar terms required by the zero-vorticity condition. Equivalently, when the equation is written in scalar form, these corrections appear as an imaginary contribution to the effective potential. At leading order our system reduces to the usual Schrödinger–Poisson formulation, while at 1PF order it provides a relativistic extension of the Schrödinger description of cold matter dynamics.
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Solar and Stellar Astrophysics

XP-TEAL: Gaia XP tool for emission and absorption lines. I. Balmer lines in open clusters

J. M. Carrasco, M. Weiler, S. Malhotra et al. (+5 more)

Context. The third Gaia data release (Gaia DR3) includes blue and red low-resolution spectrophotometry for more than 200 million sources. These Gaia XP spectra are represented by sets of coefficients multiplying linear combinations of basis functions related to Hermite functions. In a previous work we introduced a method that maximally exploits the information encoded in the Gaia spectrophotometric coefficients in order to identify absorption and emission lines. Aims. Our aim is to detect hydrogen Balmer emission and absorption lines in stars belonging to open clusters included in the released Gaia DR3 blue and red spectrophotometry, and to characterise the Balmer line strengths as a function of colour. Methods. We refined our XP tool for emission and absorption lines (XP-TEAL), using derivatives of the internal spectral coefficients to analyse hydrogen Balmer lines in the Gaia DR3 XP spectra. We tested our results using stars in open clusters, considering both absorption and emission features. Results. The analysis of the hydrogen lines in the spectra of open cluster stars allows us to assess the performance and limitations of the method. We find an empirical dependence of the absorption-line equivalent widths on the intrinsic colour of the stars, which allows us to derive precise colour excesses caused by interstellar extinction. We also identify 1256 stars with emission lines, 356 of which have not previously been reported in the literature. Conclusions. We successfully tested our XP-TEAL code on stars in clusters and have made both the source code and the online version available to the community. Despite the low resolution of Gaia spectrophotometry, our code is able to extract useful line information.
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All authors J. M. Carrasco, M. Weiler, S. Malhotra, F. Anders, C. Jordi, E. Masana, J. Castañeda, F. Boix

Astrophysics of Galaxies

Deep Learning Segmentation of Spiral Arms and Bars for 600,000 Galaxies in DESI

Ashley Spindler, Mike Walmsley, Karen L. Masters et al. (+4 more)

We present a catalogue of segmentation maps identifying the extent of spiral arms and bars of 639,636 galaxies in the DESI Legacy Survey. To produce these maps, we have trained a deep U-net-style neural network using the pixel masks from the Galaxy Zoo: 3D citizen science project. The resulting data products are "soft" segmentation maps, which show the confidence of the model that a pixel lies within the spiral arms or bars of a galaxy. In this paper we detail the sample selection from DESI-LS using the machine classifications from Galaxy Zoo: DESI, the architecture of the U-net model–dubbed ZooBot:3D. We demonstrate the ability of the model to identify spiral arms and bars in a wide range of face-on disks, and identify an emergent ability to identify rings–despite only a small number of ring-type galaxies being present in the training data. Finally, we discuss the practical application of these data products to photometric imaging and IFU spectroscopy. The ZooBot:3D dataset is available for use publicly, and contains the full catalogue presented in this paper, along with cross-matched subsamples for the MaNGA and SAMI IFU surveys.
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All authors Ashley Spindler, Mike Walmsley, Karen L. Masters, Tobias Géron, Izzy L. Garland, B. D. Simmons, Jürgen J. Popp

Earth and Planetary Astrophysics

The capability of CSST in characterizing planetary atmospheres. I. transmission spectroscopy of hot Jupiters

Zibo Liu, Wei Wang, Meng Zhai et al. (+9 more)

Transmission spectroscopy has become a primary tool for probing exoplanetary atmospheres, enabling constraints on their chemical compositions and providing limited information on their thermal properties. We assess the potential of the upcoming Chinese Space Station Telescope (CSST) for exoplanet atmospheric characterization through transmission spectroscopy. Theoretical spectra of hot gas planets are generated and used to simulate slitless spectroscopic observations with the CSST across the ultraviolet-to-near-infrared range. Atmospheric retrievals performed on the simulated data are compared with the input models to assess the robustness and accuracy of parameter determinations. We find that multi-band observations across three wavelength channels, each with two transits can place meaningful constraints on key atmospheric parameters. For multi-band observations that account for correlated (red) noise, future CSST observations are expected to achieve constraints that are comparable to, or in some cases slightly weaker than, those of the Hubble Space Telescope (HST), depending on the noise level and observing strategy. We conclude that CSST will provide unique and complementary constraints on the chemical compositions and physical properties of exoplanetary atmospheres, particularly for atomic species, metal-bearing molecules, and scattering processes accessible in the UV and optical, thereby complementing JWST's infrared sensitivity to molecular species.
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All authors Zibo Liu, Wei Wang, Meng Zhai, Jinpeng Wang, Qinglin Ouyang, Fei Yan, Guo Chen, Dongdong Ni, Yong Zhao, Yujuan Liu, Fei Zhao, Gang Zhao

Solar and Stellar Astrophysics

Minimising magnetic activity effects in PLATO observations: insights from the Sun-as-a-star

Jérôme Bétrisey, Anne-Marie Broomhall, Sylvain N. Breton et al. (+4 more)

Recent studies showed that magnetic activity effects in solar-type stars can substantially bias seismic inferences, particularly age estimates, regardless of modelling strategy or surface treatment. We quantified how magnetic activity effects in the Sun-as-a-star are smoothed by temporal averaging by analysing 182.5-, 365-, 730-, and 1460-day time series from the BiSON network and the GOLF instrument. We estimated the activity-induced systematic uncertainty using two metrics and compared results across baselines to evaluate how the observing window shapes activity-induced biases. Solar-cycle signatures persist even in 1460-day windows. The suppression of magnetic activity effects with increasing baseline is non-monotonic: one- and four-year windows reduce biases far more effectively than shorter baselines in most cases, whereas 730-day windows provide only limited improvement over 365-day ones. Improvements arise from enhanced frequency determination (dominant at 365 days) and from increasingly efficient temporal averaging of the activity cycle (dominant at 1460 days). In contrast, 730-day is an intermediate regime: frequency accuracy has already plateaued and the observing window remains too short to smooth out cycle-related variability. On average, we find that magnetic activity effects decrease by 24%, 12%, 30%, and 38% when transitioning from 182.5 to 365 days, 365 to 730 days, 730 to 1460 days, and 365 to 1460 days for frequency-based fits; the corresponding improvements for ratio-based fits are 13%, 14%, 20%, and 31%. These results indicate that a continuous single-field four-year PLATO observing programme would provide the most effective suppression of magnetic-activity biases for solar analogues, whereas a 2+2-year strategy (in two distinct fields) is significantly more sensitive to magnetic effects, with limited gains between 365- and 730-day windows.
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All authors Jérôme Bétrisey, Anne-Marie Broomhall, Sylvain N. Breton, Eva Panetier, Rafael A. García, Henry Davenport, Oleg Kochukhov

Astrophysics of Galaxies

Co-evolution of bar and spiral arms in TNG50 simulations using Information Theory

Anagha A G and Arunima Banerjee

Using Information Theory, we investigate the co-evolution of bars and spiral arms in barred-spiral galaxies from the cosmological magneto-hydrodynamic Illustris TNG50 simulations. We first calculate Mutual Information (MI) between a structural or kinematic parameter of the bar (bar strength $A_{2bar}$, bar length $r_{bar}$, bar pattern speed $\Omega$) and that of a spiral arm (spiral strength $A_{2spiral}$, spiral arm pitch angle $\Psi$). We calculate MI in two different galaxy samples: (i) one forming bars before spirals (ii) other forming spirals before bars. We note, spirals form immediately after bars in the first sample, whereas bars form 1.7 Gyrs after spirals in the second. We find a high mean MI value in each of these samples (0.4 - 0.5), and in the combined sample (0.4-0.8), confirming a fair degree of association of the bar and the spiral arm. To identify whether the bar or the spiral arm effectively drives their co-evolution, we calculate the Transfer Entropy (TE) (bar-to-spiral TE, spiral-to-bar TE), from the time series data of each of the above bar-spiral parameter pairs. We find that the median bar-to-spiral TE and spiral-to-bar TE values vary between $ 0.33$ and $ 0.42$ for each galaxy sample, comparable to those of the combined sample. A similar trend was observed in our calculated Liang information flow rates. Our novel approach may possibly indicate that the bar and the spiral arm regulate their co-evolution on an equal footing.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Generalized Unimodular Gravity and Cosmological Perturbations

Júlio C. Fabris and Alexander Yu. Kamenshchik

The generalized unimodular theory is revisited and its consequence for cosmology is discussed. The usual matter components of the universe are obtained in a pure geometric way. This result gives a new perspective to the studies of the dark sector of the universe. A background and perturbative analysis are carried out, recovering the corresponding results obtained through the general relativity theory but with a different interpretation.
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Solar and Stellar Astrophysics · Cross-listed from physics.plasm-ph

The Effect of Anomalous Resistivity on Tearing Instability

D. Tsiklauri

We study the modification of classical tearing instability due to anomalous resistivity by incorporating a variable, second-order resistivity model into the resistive magnetohydrodynamics (MHD) framework. We evaluate the resulting {weakly non-linear boundary-layer scaling laws under a localized current-feedback mechanism}. By extending the {inner-layer analysis to capture localized current feedback}, we resolve localized spatial singularities ($\delta$ and $\delta'$) at the threshold boundary. These singularities generate unexpected matching jump conditions, demonstrating an early-stage phase-slip layer that forces a hyperbolic, time-dependent growth rate divergence prior to macroscopic saturation. Physical estimates for fusion devices and solar flares prove that this {consistent weakly non-linear matching formulation} triggers an abrupt transition into the explosive reconnection regime, offering an exact analytical resolution to the long-standing solar and tokamak flare/disruption “trigger problem,” respectively. Finally, a comparative analysis using a truncated linear expansion of the threshold model regularizes the singular behavior, confirming that the explosive finite-time singularity is uniquely driven by the higher-order non-linear current feedback.
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Astrophysics of Galaxies

The gas kinematics in 70 {\mu}m dark molecular clumps with ammonia

Chao Ou, Shanghuo Li, Junzhi Wang et al. (+5 more)

We present the investigation of the gas kinematics and assess the evolutionary stages of dense cores embedded in four infrared dark clouds (IRDCs) using the NH$_3$(1,1) and NH$_3$(2,2) lines obtained from the VLA and GBT observations. There is no 1.3 cm continuum emission counterpart in 1.3 mm continuum emission revealed by the SMA toward these IRDCs. The low production rate $N_{\rm uv} \sim 10^{44}$ s$^{-1}$ of Lyman continuum photons, indicates that the four IRDCs are in very early evolutionary stages, in which free–free emission is still absent. We have identified 61 dense cores at the size scale of $\sim$0.1 pc using the inner satellite groups of NH$_3$(1,1) line. Among them, 38 dense cores exhibit a single velocity component, while 23 dense cores show multiple velocity components. We find that the nonthermal velocity dispersion ($\sigma_{\mathrm{non}}$) increases with increasing radial distance from the center of dense core within the inner 0.1 pc toward eight dense cores, indicating that the turbulence is likely dissipated toward the center of these dense cores. In addition, two dense cores in AGAL031.024+00.262 and one core in AGAL024.314+00.086 exhibit nearly sonic motions on a small scale of 0.01 pc. The weakening of nonthermal support against gravity suggests that these dense cores are close to gravitational collapse or are already collapsing. Conversely, there are seven dense cores in AGAL031.024+00.262 showing a decrease in $\sigma_{\mathrm{non}}$ with increasing radial distance from the center. By comparing this trends with the outflow revealed by CO J=2-1 line, we find that these cores are likely associated with embedded star formation activities. Higher angular resolution observations on sub-parsec scales are essential to reveal the transition from thermal to nonthermal-dominated regions, especially in dense cores associated with multiple velocity components.
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All authors Chao Ou, Shanghuo Li, Junzhi Wang, Yuqiang Li, Shuting Lin, Ian W. Stephens, Qizhou Zhang, Bo Zhang

Astrophysics of Galaxies

Optical Variability as a Probe of Hidden Nuclear Activity in Type 2 AGNs

Maša Lakićević

Optical variability in Type 2 active galactic nuclei (AGNs) is rarely explored because the direct accretion-disk continuum is obscured by circumnuclear dust. Nevertheless, detectable optical variations are present in multi-epoch surveys such as SDSS Stripe~82, indicating that some component of the nuclear emission is observed indirectly, for example through scattering or partial transmission. This study explores whether this variability is statistically connected to spectroscopic parameters of the narrow-line region (NLR), using the ALPAKA catalogue of spectral measurements. A subsample of 412 Type 2 AGNs was assembled by crossmatching SDSS Stripe 82 multi-epoch variability measurements in the $u,g,r,i,z$ bands with the ALPAKA spectroscopic catalogue. Correlations were then computed between the root-mean-square (RMS) variability amplitudes and the corresponding emission-line luminosities, kinematic widths and equivalent widths (EWs). Significant anti-correlations are found between the RMS amplitudes and [O III] 4949, [O III] 5007, [N II] 6548 and [NII] 6584 line luminosities. Velocity dispersions ($\sigma$) and EWs of forbidden-lines [O III] 5007 and [N II] 6584 also show moderate anti-correlations with RMS. The results demonstrate that even in obscured AGNs, optical variability carries information about the hidden nucleus. The anti-correlation between RMS and line luminosity suggests a connection between accretion stability and ionising output. Anti-correlations between RMS and the [O III] and [N II] velocity dispersions indicate a secondary correlation between optical RMS variability and the integrated kinematic state of the NLR. In addition, the anti-correlation between RMS and EW shows that the EW variations are primarily driven by changes in the continuum level, while the narrow-line flux itself remains effectively constant on the relevant timescales.
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Earth and Planetary Astrophysics · Cross-listed from physics.geo-ph

Resonant lunar tides of Earth's core and basal magma ocean

Murray B.C. Kiernan, Hamish C.F.C. Hay, David W. Rees Jones et al. (+2 more)

Earth's magnetic field is generated by fluid motion in the liquid-metal core and has been active for billions of years. However, prior to the onset of inner-core growth, the sources of mechanical power that drove the geodynamo remain uncertain. During this period, the core may have been overlain by a basal magma ocean (BMO), creating two immiscible fluid layers separated by a density interface, beneath the solid mantle. We develop a theory for lunar tides in this core–BMO system, in which the tidal potential acts on the density contrast between the two layers. The resulting dynamics differ fundamentally from previous models driven by imposed deformation of the core's bounding envelope. In the inviscid limit, the response transitions from an equilibrium tide to an interfacial gravity wave as forcing frequency increases. The two regimes are separated by a resonance that occurs when the forcing frequency matches the natural frequency of the degree-2, order-2 interfacial mode. The inviscid core flow is formally identical to the canonical elliptical vortex, linking the problem to the theory of elliptical instability. Finite viscosity regularises the resonance, introduces phase lag and generates oscillatory boundary layers. Combined with parameterised models of lunar recession and BMO crystallisation, the theory predicts enhanced core-boundary ellipticity, core-flow speed, magnetic Reynolds number and instability metrics, particularly near resonance. These results identify a previously unexplored mechanism for tidally driven flow in differentiated planetary bodies and show that a BMO can enhance tidal coupling to the core, potentially contributing to dynamo action.
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All authors Murray B.C. Kiernan, Hamish C.F.C. Hay, David W. Rees Jones, James F.J. Bryson, Richard F. Katz

Astrophysics of Galaxies

Groups of Dwarf Galaxies in the Local Universe

Sanjaya Paudel, Cristiano G. Sabiu, Suk-Jin Yoon et al. (+3 more)

We present a systematic search for dwarf-galaxy groups in the local Universe ($z<0.02$), identifying 28 systems containing at least four spectroscopically confirmed members selected from the SDSS and DESI surveys. Group membership is assigned based on projected separation -within 300\,kpc from the most massive galaxy (designated the “central”) -and a relative line-of-sight velocity difference of less than 200\,km/s. The sample has a median redshift of $z=0.0131$ ($\sim55$\,Mpc) and a median central stellar mass of $1.7\times10^{9}\,M_\odot$, firmly placing these systems in the low-mass regime. In total, 28 groups contain 129 dwarf galaxy members, with a median stellar mass of $1.63\times10^{8}\,M_\odot$. The median $r$-band apparent magnitude of the member dwarfs is 17.38\,mag, slightly fainter than the spectroscopic observation limit of the SDSS main spectroscopic survey. Remarkably, several groups are centered on galaxies with stellar masses as low as $\sim10^{8}\,M_\odot$, comparable to the Fornax dwarf spheroidal, demonstrating that even very faint galaxies can host bound satellite systems. Most groups exhibit low velocity dispersions ($\sigma_{v}<50$\,km/s), consistent with being gravitationally bound. The inferred dynamical masses span $\sim10^{10}-10^{12}\,M_\odot$, while the corresponding three-dimensional velocity dispersions ($\sigma_{3D}$) fall between 50 and 100\,\kms, characteristic of dynamically cold, low-mass halos. Our results provide empirical constraints on small-scale structure formation and show strong consistency with predictions from cosmological volume simulations, supporting the picture that dwarf galaxies can serve as central hosts for their own satellite systems embedded within extended dark-matter halos.
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All authors Sanjaya Paudel, Cristiano G. Sabiu, Suk-Jin Yoon, Daya Nidhi Chhatkuli, Jaewon Yoo, Nau Raj Pokhrel

Cosmology and Nongalactic Astrophysics

Tomography of the gamma-ray sky from cross-correlation with DESI DR2 and unWISE galaxies

Alex Krolewski, Neal Dalal, Will J. Percival et al. (+39 more)

We study the origin of extragalactic gamma-ray emission observed by Fermi-LAT, using the cross-correlation of the gamma-ray sky with maps of large-scale structure provided by the DESI and unWISE surveys. Tomographic cross-correlation reveals the bias-weighted redshift distributions of gamma-ray sources. We first illustrate this method by cross-correlating detected gamma-ray point sources with large-scale structure. We find a significant cross-correlation and infer a point source redshift distribution broadly consistent with the distribution of identified optical counterparts previously reported in the literature, as well as a similar linear bias ($b \approx 2$) to massive galaxies that host bright active galactic nuclei. We then study the clustering of the Fermi unresolved gamma-ray background (UGRB), both in auto-correlation and in cross-correlation with large-scale structure. We detect the cross-correlation of the UGRB and LSS at $\sim 10\sigma$ in total, with highly significant detections from both DESI and unWISE. Our measurements suggest that the redshift distribution of the UGRB is broadly consistent with the redshift distribution of detected point sources. Additionally, we find a relatively weak amplitude for the cross-correlation with large-scale structure at z < 2, suggesting a significant fraction of the UGRB does not come from z < 2 large-scale structure. A natural candidate is contamination of from residual Galactic emission, and our best estimate of the contamination level derived from the UGRB auto-spectrum suggests that the mean bias of UGRB sources is indeed quite similar to the bias of detected Fermi point sources. However, we cannot exclude additional emission from gamma-ray sources at high redshift, z > 2, and we suggest that cross-correlation with tracers at z > 2, including CMB lensing, would be the ideal way to determine the fraction of z > 2 emission.
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All authors Alex Krolewski, Neal Dalal, Will J. Percival, Elena Pinetti, J. Aguilar, S. Ahlen, S. BenZvi, D. Bianchi, D. Brooks, T. Claybaugh, A. Cuceu, A. de la Macorra, P. Doel, S. Ferraro, A. Font-Ribera, J. E. Forero-Romero, E. Gaztanaga, S. Gontcho A Gontcho, G. Gutierrez, J. Guy, D. Huterer, M. Ishak, R. Joyce, A. Kremin, O. Lahav, M. Landriau, L. Le Guillou, M. E. Levi, M. Manera, A. Meisner, R. Miquel, A. D. Myers, S. Nadathur, F. Prada, I. Perez-Rafols, G. Rossi, E. Sanchez, D. Schlegel, J. Silber, D. Sprayberry, G. Tarle, B. A. Weaver

Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Ultraviolet Structure of Real-time Gravitational Wave Linear Response in a Resonant Scalar Field

Han Lai and Atsuhisa Ota

We study the real-time linear response of gravitational waves in a time-dependent resonant scalar field in a Minkowski background. In the Schwinger-Keldysh formalism, we develop an adiabatic regularization scheme for unequal-time correlation functions and use it to extract the ultraviolet structure of the one-loop response. The leading divergence reproduces the familiar $\Box^2 h_{ij}$ structure, whereas the time-dependent background induces additional local divergences proportional to $\Box h_{ij}$, $\partial_0 h_{ij}$, and $h_{ij}$. These are renormalized by local counterterms associated with the Weyl-squared term, a time-dependent Ricci-scalar term, and a time-dependent cosmological constant. We also compare the renormalization of the linear response with that of the tadpole stress tensor and find a mismatch beyond leading adiabatic order in the present toy model. By considering a covariant completion of the resonance, we further argue that this mismatch is tied to the off-shell nature of the fixed background, and is expected to disappear once the background is treated on shell.
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Solar and Stellar Astrophysics

Investigation of Solar Wind Speed Characteristics Using IPS Observations and the PFSS+SCS Model

Kyogo Tokoro, Munehito Shoda and Shinsuke Imada

Understanding the relationship between solar wind speed and global coronal magnetic field is essential for space-weather forecasting and provides key diagnostics of the underlying acceleration mechanisms. Most observational studies to date have relied on near-ecliptic measurements dominated by slow wind, and the full range of wind speed, including fast wind, is insufficiently explored. Interplanetary scintillation (IPS) observations offer global coverage of wind speed; however, previous IPS-based studies have relied solely on the potential field source surface (PFSS) model, which does not adequately reproduce key features of the heliospheric magnetic field, potentially leading to the poor connectivity between the solar wind and its coronal source regions. Here we perform a comprehensive statistical analysis of the wind speed using IPS observations combined with PFSS and the Schatten current sheet (SCS) model. We find that the parameter f_SS/B_sun bifurcates the solar wind into two distinct groups: one showing a strong negative correlation and the other showing no correlation. This grouping is better organized by the footpoint magnetic field strength and the distance from coronal hole boundary (DCHB) than by solar magnetic activity, suggesting that the two groups may reflect fundamentally different acceleration mechanisms.
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Astrophysics of Galaxies

The Milky Way's Missing In-Situ Halo

Madeline Lucey, Robyn E. Sanderson, Alexander H. Riley et al. (+3 more)

The Milky Way's stellar halo preserves a record of its mass assembly history, encoding accretion events in its structural properties. Among the most prominent of these features is a strong break in the halo density profile at $\approx$20-30 kpc, long attributed to the apocenter pile-up of stars from the Gaia-Enceladus/Sausage merger. However, whether this interpretation is consistent with state-of-the-art cosmological simulations remains unclear. In this work, we compare the Milky Way's measured stellar halo density profile between galactocentric radii of $1\unicode{x2013}100$ kpc to those of Milky Way-mass galaxies from the FIRE-2 and Auriga cosmological zoom-in simulation suites, spanning a total of 24 simulated galaxies. We find that simulated halo profiles are significantly steeper than Milky Way measurements within $\approx$15 kpc, and that profile breaks are rare in simulations and never as strong as the Milky Way's. Of the three galaxies with statistically significant breaks, only one exhibits a break attributable to apocenter pile-up of an accreted merger remnant. Decomposing the simulated profiles, we find that the accreted halo profiles are broadly consistent with Milky Way measurements, while the in-situ halo dominates within $\approx$20 kpc and drives the discrepancy. These results raise a compelling question: where is the Milky Way's in-situ halo? The origin of this tension may reflect systematic biases in current halo measurements, an overproduction of early spheroidal star formation in cosmological simulations, or more fundamental differences in the underlying physics (e.g., dark matter) governing the assembly and structure of the inner Galaxy.
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All authors Madeline Lucey, Robyn E. Sanderson, Alexander H. Riley, Andreia Carrillo, Jenna Samuel, Emma Tasso

Solar and Stellar Astrophysics

Near-Sun Switchbacks Show Statistical Signatures of Solar Activity

Sneha Pandit, Thierry Dudok de Wit, Clara Froment et al. (+3 more)

The large amplitude, Alfvénic deflections in the solar wind, called magnetic switchbacks, are a ubiquitous feature of the inner heliosphere, yet their origin and variability remain poorly understood. We investigate the dependence of large amplitude magnetic fluctuations in the inner heliosphere on both heliocentric distance and global solar activity. Using Parker Solar Probe observations, we quantify switchback deflections through their normalised deflection angle $z$. We examine both their distribution and the probability of large events, combining radial binning, sunspot-number-based activity classification, and regression analysis. We find a statistically significant but weak dependence of switchback properties on solar activity, with a decrease in large deflections at higher activity levels, alongside a modest increase with heliocentric distance. The weak activity trend suggests that multiple processes act simultaneously. Solar-cycle variations in coronal magnetic topology may modulate switchback generation at the source, while nonlinear in situ effects in the solar wind may partially evolve these signatures. Our results indicate that switchbacks retain only a limited imprint of solar activity, reflecting a coupled interplay between coronal origin and in situ evolution. This study provides a quantitative framework to disentangle activity and radial effects, and highlights the need for multi-parameter and multi-spacecraft analyses to fully understand the origin and evolution of switchbacks.
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All authors Sneha Pandit, Thierry Dudok de Wit, Clara Froment, Durgesh Tripathi, Vishal Upendran, Gabriel Ho Hin Suen

Cosmology and Nongalactic Astrophysics

Benchmarking Exact, GP-Emulated, and Simulation-Based Inference for Late-Time Cosmology

Sai Swagat Mishra

Forthcoming cosmological surveys require inference pipelines that are both statistically reliable and computationally scalable. In this work, we perform a systematic comparison of three complementary inference strategies for late-time $\Lambda$CDM cosmology: exact Markov Chain Monte Carlo (MCMC), Gaussian Process (GP)-assisted MCMC, and neural Simulation-Based Inference (SBI). Using a common analysis framework based on Cosmic Chronometers, DESI DR2 baryon acoustic oscillation measurements, and the Pantheon+ Type Ia supernova compilation, we consider two dataset combinations of increasing complexity, namely CC+DESI and CC+DESI+PP, under identical cosmological assumptions and priors. For CC+DESI, both GP emulation and SBI reproduce the exact posterior constraints on $(H_0,\Omega_{m,0})$ to better than $0.3\sigma$. For the more constraining CC+DESI+PP combination, modest method-dependent shifts emerge, reaching at most $\sim1.5\sigma$ in a single parameter. Despite these differences, all methods recover a nearly identical expansion history, with percent-level agreement across the full redshift range. From a computational perspective, GP emulation accelerates model evaluations but remains limited by MCMC sampling, whereas SBI achieves order-of-magnitude reductions in total runtime through amortized posterior learning. We further investigate the convergence of SBI as a function of simulation budget and identify the number of simulations required to obtain stable posterior constraints. Overall, our results demonstrate that accelerated inference techniques can deliver reliable cosmological constraints for realistic late-time datasets considered here at a fraction of the computational cost of conventional likelihood-based analyses.
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High Energy Astrophysical Phenomena

Discovery of Unusual Jet Orientation Variations in the Microquasar GRS 1915+105

Xi Yan, Lang Cui, Wu Jiang et al. (+6 more)

We report large day-timescale variations in the orientation of the southeast–northwest jet in the prototype microquasar GRS 1915+105. These results are based on three-epoch East Asia VLBI Network (EAVN) observations at 6.7 GHz, obtained during giant radio flares in 2025 detected by the RATAN-600 monitoring program. Our observations reveal the smallest position angle (PA) of $118^\circ \pm 7^\circ$ ever measured for the jet in GRS 1915+105, which increases to $152^\circ \pm 2^\circ$ within 37 days. Based on the literature results, we further suggest that the jet orientation has exhibited significant variations over a PA range of $118^\circ$–$188^\circ$ since 2023. This unusual jet orientation behavior in GRS 1915+105 during its current X-ray-obscured state may arise from a warped, precessing inner accretion disk, as implied by recent X-ray spectroscopy. Notably, one image reveals a peculiar morphology in GRS 1915+105, which likely indicates lateral spreading of the approaching southeast jet. Future observations are essential to clarify the issues raised in this work.
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All authors Xi Yan, Lang Cui, Wu Jiang, Zhen Yan, Sándor Frey, Sergei Trushkin, Timur Mufakharov, Ruchika Dhaka, Shuangjing Xu

Cosmology and Nongalactic Astrophysics

Nonlinear Dynamical Regimes of Cosmological Frequency Combs

Madhurendra Mishra, Oem Trivedi and Adarsh Ganesan

We study the emergence of Cosmological Frequency Combs (CFCs) in a quintessence cosmology with an exponential potential using a dynamical systems formulation. Expressing the evolution equations in expansion-normalized variables yields an autonomous nonlinear system that supports time-periodic attractors corresponding to limit cycles, producing comb like spectral structures in cosmological observables without external periodic forcing. Numerical simulations reveal transitions between single frequency, comb like and chaotic regimes controlled by the fundamental frequency, background equation of state parameter, and initial conditions. Coherent comb structures arise only within well defined dynamical windows, while very low frequencies and unfavorable initial conditions suppress phase locking. These results show that CFCs naturally emerge from nonlinear cosmological dynamics and motivate further study of their possible observational implications.
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Astrophysics of Galaxies

A 1.3 cm spectral line study of the W33 region

Kadirya Tursun, Christian Henkel, Jarken Esimbek et al. (+14 more)

At a distance of 2.4kpc, W33 is one of the most prolific sources of molecular line emission, and it is an excellent research target for a centimeter spectral line search. We carried out a 1.3cm spectral line survey in the frequency range 18-26GHz. The lines we identified include 44 radio recombination lines (RRLs) and 24 molecular lines, excluding transitions from the main isotopolog of NH3. The RRLs are associated with the ionized gas from W33Main. Intensity ratios between RRL pairs with varying differences in the principal quantum number $n$ (i.e., $\Delta n$) from the same element at adjacent frequencies agree with ratios expected under conditions of local thermodynamical equilibrium. In spite of a resulting helium-to-hydrogen abundance ratio (equal emitting volumes assumed) of (10.7$\pm$1.8)%, which is consistent with expectations, helium shows broader turbulent line widths than hydrogen. The difference amounts to a few kilometers per second, hinting that the spatial distributions are slightly different. The molecular lines are attributed to nine different species (CH3OH, HC3N, SiS, c-C3H2, CH3CN, NH2D, HNCO, H2O and CCS). Rotation temperatures and column densities were derived from CH3OH transitions using rotational temperature diagram analysis. Maser emission produced by water vapor and methanol have been observed in W33Main, W33A, and W33B. Our survey discovered a CH3OH(10$_{2,8}$-10$_{1,9}$E) maser in W33Main. Toward W33B1, the fractionated deuterium-to-hydrogen ratio (D/H) deduced from para-NH2D/NH3 is estimated to be $\lesssim$(1.0$\pm$0.2)$\times$10$^{-3}$. For the other molecular W33-hotspots, 3$\sigma$ upper limits are (5.0$\pm$0.4)$\times$10$^{-3}$. At linear scales of (0.5pc), fractional abundances and excitation temperatures do not reach values close to those in well-established hot cores, but higher-resolution measurements may alter this picture.
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All authors Kadirya Tursun, Christian Henkel, Jarken Esimbek, Gang Wu, Dalei Li, Xindi Tang, Jianjun Zhou, T. L. Wilson, Friedrich Wyrowski, Rainer Mauersberger, Katharina Immer, B. Winkel, Yuxin He, Dongdong Zhou, Andrey M. Sobolev, Toktarkhan Komesh, Hailiang Shen